Adaptive antenna array and method of controlling operation thereof

ABSTRACT

An adaptive antenna array ( 14 ) includes a muliplicity of antenna elements ( 12   a - 12   k   , 48   a - 48   k ) responsive to uplink communications ( 16   a - 16   k ) and arranged to support directional-orientated downlink communication to subscriber units ( 18 ). The adaptive antenna array ( 14 ) is operationally responsive to a signal processor ( 28 ) that co-operates with direction of arrival estimation logic ( 36 ) to assess an angle of arrival of uplink communications incident to the array. To avoid inter-cell interference, especially during early stages of a call, the signal processor operates to ensure that a wide area downlink beam ( 108 ) is provided for a downlink path to an addressed subscriber unit. With time and/or with reported ( 68,84 ) downlink quality of service (QoS) metrics, the signal processor ( 28 ) regulates ( 74, 92, 96 ) a width of the downlink beam by altering the number of antenna elements used to support the downlink beam, thereby altering the downlink beam aperture. Generally, with time, more antenna elements ( 92 ) are used and so the beam is narrowed, although in-call fluctuations in downlink quality of service are dynamically addressed by the signal processor ( 28 ) by either narrowing or broadening the width of the downlink beam by respectively switching antenna elements ( 12   a - 12   k   , 48   a - 48   k ) into ( 92 ) or out ( 96 ) of the adaptive antenna array ( 14 ), as shown in FIGS.  3   a  and  3   b.

BACKGROUND TO THE INVENTION

[0001] This invention relates to an adaptive antenna array and a methodof controlling the operation thereof. The present invention isparticularly, but not exclusively, applicable to a method and apparatusfor maximising Quality of Service (QoS) to a subscriber unit in a mobilewireless telecommunications system. More particularly, the presentinvention is applicable to operational use of an adaptive antenna arrayduring the establishment of a connection to a subscriber unit, althoughit can be applied dynamically in an in-call scenario.

SUMMARY OF THE PRIOR ART

[0002] Adaptive antenna beam forming architectures provide a directionaldownlink beam based on information derived from uplink beammeasurements. An attainable degree of prediction accuracy of a downlinkestimate limits the capacity and frequency re-use that is achievable byany adaptive antenna network since an explicit downlink channel estimateis not available to the base station at which the antenna network islocated. More especially, the uplink channel and the downlink channelmay be instantaneously, or for short periods, subject to differentpropagation conditions (such as multi-path propagation, fading and thelike). Consequently, any estimate pertaining to an angular/directionaldisplacement of a subscriber unit relative to an antenna array that isreliant upon such measured channel information will appear different. Inpractice, therefore, the estimated direction of a subscriber unit (e.g.a mobile station) has an associated uplink to downlink directional error(θ_(e)) because the uplink and the downlink are not subject to the samepropagation conditions when the uplink and downlink carrier frequenciesare separated.

[0003] With time, however, a statistical averaging effect between theuplink and downlink causes a convergence of direction/angle of arrivalestimates derived from physically distinct paths (typically supported bydifferent carrier frequencies). Indeed, in most existing systems and inview of this convergence phenomenon, the uplink directional estimate isused throughout the call in view of the uncertainty in the existence ofany correlation between the uplink and downlink estimates.

[0004] Generally, in order to obtain a downlink directional estimate, anuplink signal is processed in such a manner that certain parameters,such as channel (particularly carrier) to interference ratios (C/(I+N)),are optimised. This directional processing may be achieved byselectively combining all of the different antenna elements in the arrayuntil an optimum combination is found. Certain preferred or pre-setalgorithm combinations, known to the skilled addressee, are used fordetermining the principle direction (θ_(u)) of the uplink for the mobilestation in question. Then, once the principle direction, i.e. the angleof arrival, is established, energy in the downlink beam is steeredtowards an estimated downlink direction (θ_(d)) of the subscriber unit,regardless of the subscriber's actual direction relative to the antennaarray. Steering therefore hopes to benefit from sufficient statisticalaveraging in the uplink and downlink multi-path for the physical andradio frequency directions to be equivalent.

[0005] Steering may be achieved by determining the fixed beam for aButler beam-former, or by determining the adaptive weights for abaseband beam- former.

[0006] By way of more specific example, a direction-finding searchregime in the base station looks to an instantaneously or time-averagedmeasured uplink direction metric to use as a basis for a downlinkdirectional estimate. One problem with this procedure is that it canlead to a dramatic alteration of the estimated direction in successiveprinciple downlink estimates. More specifically, attempts to track amoving mobile unit by using such instantaneous snapshots can beineffective and/or complex (i.e. processing intensive) because theuplink to downlink error is a function of the speed and propagationconditions of the mobile unit.

[0007] Although adaptive antennas, in general, reduce co-channelinterference in an antenna network when the uplink and downlinkdirectional estimates are the same as the downlink direction, any errorbetween the actual downlink direction and the downlink estimate causes asignificant reduction in the C/(I+N) and an increase in overall systeminterference. In a worst case scenario, a narrow beam downlink carriercould be aligned in an opposing direction to the actual position of thesubscriber unit. In this instance, the subscriber unit (in conventionfashion) provides a report to the base station indicating poor QoS (orfailure to receive an expected transmission). Since the system generallyoperates on an interference limited basis, the base station increasespower in a subsequent narrow beam transmission to the subscriber unit;this increase in power is perceived/designed to improve QoS to thesubscriber unit. The increased power used in the narrow beam thereforehas increased reach and so the carrier frequency used in the downlinkcauses adjacent splutter (i.e. co-channel and/or adjacent channelinterference) in an adjacent cell.

[0008] Even with a now increased level of power in the narrow beamdown-link transmission, the addressed subscriber unit may still registeran unacceptably low QoS and so the subscriber again effectively requestsimproved service by reporting the low QoS (be this received signalstrength, bit error rate or the like). With the base station unable toresolve physical displacement of the addressed subscriber unit (eveninferred through timing advance), the base station again increases powerin its subsequent downlink transmission to the subscriber unit.Moreover, this increased power downlink transmission is likely to stillbe directionally incorrect since directional convergence between theuplink and downlink estimates may not yet have taken place. Theincreased power in the carrier reaches yet further into at least thenext adjacent cell and perhaps beyond. Therefore, at some point,downlink power concentrated in an originally narrow beam becomes asignificant problem because, with ever-increasing radial displacement,the area covered by the narrow beam increases. System interferencetherefore increases because the power within the narrow beam acts tooffset the affects of signal attenuation.

[0009] In other words, with the downlink direction wrongly estimated,operation of the system to maximise/improve QoS results in more powerbeing steered in an incorrect direction, thereby increasing systeminterference (as a whole) until downlink and uplink directionalestimation convergence occurs. At this point of convergence, the basestation transceiver (BTS) will only need to transmit a lower power forthe mobile to achieve its desired QoS; this is because of aperture gain.

[0010] The problems associated with interference in cellularcommunications systems and the issues to be considered in a cellularsystem employing frequency reuse are generally described in the textbook “The Global System for Mobile Communications” by Michel Mouly andMarie-Bernadette Pautet, pages 599 to 601.

SUMMARY OF THE INVENTION

[0011] According to a first aspect of the invention there is provided anadaptive antenna arrangement for generating a downlink beam, theadaptive antenna arrangement comprising: a plurality of antennaelements; and a controller for controlling formation of the downlinkbeam, the controller characterised in that the controller is arranged toadjust, with time, a number of antenna elements active in the formationof the downlink beam thereby to vary, in use, a beam width of thedownlink beam.

[0012] In a preferred embodiment, the controller is operationallyresponsive to quality of service metrics of the downlink beam, andwherein the controller is arranged to vary the beam width depending uponthe quality of service metrics. Moreover, generally, the controller isarranged to vary the beam width depending upon relative variations inthe quality of service metrics.

[0013] In another embodiment the controller is arranged to vary the beamwidth and direction thereof in response to convergence between angle ofarrival estimates for downlink and uplink paths.

[0014] As will be understood, particular features of the variouspreferred embodiments may be actioned independently in or combination toprovide enhanced operation and an improved decision-making process.

[0015] In a second aspect of the present invention there is provided anadaptive antenna network providing downlink communication to a mobilestation, the adaptive antenna network comprising: two or more antennaelement adapted to be switched in and out of the adaptive antennanetwork as required; control logic for switching antenna elements in andout of the adaptive antenna network; a downlink communications channelfor downlink communication from the antenna network to the mobilestation, which channel can be measured by one or more Quality of Service(QoS) metrics and which channel is constrained to operate withinpredetermined QoS parameters; wherein the mobile station measures apredetermined QoS metric of the downlink communication and returns a QoSmeasure to the control logic; and wherein the control logic switches atleast one antenna element, if available, into the adaptive antennanetwork if the QoS measure is within the predetermined QoS parameters orswitches at least one antenna element, if available, out of the adaptiveantenna network if the QoS measure is outside the predetermined QoSparameters;

[0016] In a third aspect of the present invention there is provided acellular communication system comprising: a base station having controllogic responsible for establishing and maintaining a downlink channelresource; an antenna array comprising a plurality of antenna elements,the antenna array and the plurality of antenna elements operationallyresponsive to the control logic, the plurality of antenna elements, inuse, radiating at least one directional-orientated downlink channelresource therefrom and wherein formation of the at least onedirectional-orientated downlink channel resource is controlled by thecontrol logic; the cellular communication system characterised in that:the control logic includes means for adjusting, with time, a number ofantenna elements active in the formation of the at least onedirectional-orientated downlink channel resource, thereby to vary, inuse, a beam width of the at least one directional-orientated downlinkchannel resource.

[0017] In a further aspect of the present invention there is provided acontroller for an adaptive antenna having a plurality of antennaelements configurable, in use, to form a directional downlink beam inresponse to the controller, the controller comprising: means forcontrolling formation of the down ink beam; and means for adjusting,with time, a number of antenna elements active in the formation of thedownlink beam thereby to vary, in use, a beam width of the downlinkbeam.

[0018] In another aspect of the present invention there is provided amethod of controlling downlink communication from an adaptive antenna toa subscriber unit, the adaptive antenna having a plurality of antennaelements the method comprising: controlling dispersion of a downlinkbeam by adjusting, with time, a number of antenna elements active in theformation of the downlink beam to vary, in use, a beam width of thedownlink beam.

[0019] In yet another aspect of the present invention there is provideda method of providing downlink communication between an adaptive antennaand a mobile unit of a cellular communication system, the adaptiveantenna having two or more switchable antenna elements and control logicfor actuating switching of said antenna elements in and out of theadaptive antenna network, the method comprising: establishing a downlinkcommunications channel for downlink communication from the antennanetwork to the mobile unit and constraining the downlink communicationto operate within predetermined Quality of Service (QoS) parameters;measuring at the mobile station a predetermined QoS metric of thedownlink communication and returning a QoS measure to the control logic;and switching at least one antenna element, if available, into theadaptive antenna network if the QoS measure is within the predeterminedQoS parameters or switching at least one antenna element, if available,out of the adaptive antenna network if the QoS measure is outside thepredetermined QoS parameters.

[0020] In a particular embodiment, an adaptive antenna array includes amultiplicity of antenna elements responsive to uplink communications andarranged to support directional-orientated downlink communication tosubscriber units. The adaptive antenna array is operationally responsiveto a signal processor that co-operates with direction of arrivalestimation logic to assess an angle of arrival of uplink communicationsincident to the array. To avoid inter-cell interference, especiallyduring early stages of a call, the signal processor operates to ensurethat a wide area downlink beam is provided for a downlink path to anaddressed subscriber unit. With time and/or with reported downlinkquality of service (QoS) metrics, the signal processor regulates a widthof the downlink beam by altering the number of antenna elements used tosupport the downlink beam, thereby altering the downlink beam aperture.Generally, with time, more antenna elements are used and so the beam isnarrowed, although in-call fluctuations in downlink quality of serviceare dynamically addressed by the signal processor by either narrowing orbroadening the width of the downlink beam by respectively switchingantenna elements into or out of the adaptive antenna array.

[0021] Advantageously, a preferred embodiment of the present inventionaddresses interference problems particularly prevalent during callestablishment procedures to a subscriber unit (especially a mobile unit)from an adaptive antenna array. The present invention effectivelyensures a guaranteed minimum quality of service (QoS) at callestablishment by providing a wide area beam having a power levelappropriate to the coverage area served by the adaptive antenna array.The beam is then narrowed with time and/or QoS to move the system to aninterference-limited environment whilst seeking a guaranteed quality ofservice for the subscriber unit.

[0022] The present invention provides better translation of the uplinkestimate to the downlink estimate by assuming a worst case scenario whenthe downlink communication is initiated. An advantage of the inventionis that, depending upon the changing propagation conditions due, forexample, to the movement of a mobile station, the downlink may becontinually monitored and, consequently, optimisation of the downlinkcommunication (in terms of beam width and power control) may be manageddynamically (based, for example, on QoS) during a call.

[0023] The process of the present invention beneficially ensures thatthe measured QoS service(s) used as a metric is (are) maximised throughvarying the antenna aperture size, rather than the more time consumingprocess of trying to track or find the best downlink direction. Thepresent invention therefore provides a very simple tracking algorithmthat is significantly more stabile than a conventionalsearching/tracking algorithm. In addition, the algorithm of thepreferred embodiment of the present invention uses an average estimateof the downlink channel, since the beam is merely broadened or narrowed,and smoothes out the dramatically altering estimates which may beobtained with a tracking algorithm.

[0024] Another advantage of the invention arises in situations whereotherwise co-channel interference may impact upon the downlinkcommunication QoS. Where all base stations employ adaptive antennaarrays and networks according to the invention, all the base stationstrade off the channel against the interference. Increasing the apertureof the beam reduces the chances of encountering directional estimationerrors but increases the interference seen by the co-channel mobile.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Embodiments of the invention are described below, by way ofexample only, with reference to the following drawings, in which:

[0026]FIG. 1 illustrates variations in uplink directional estimate andthe downlink directional estimate with time;

[0027]FIG. 2 shows a block diagram of an adaptive antenna networkaccording to a preferred embodiment of the invention;

[0028]FIG. 3a shows a flow chart of preferred steps taken by controllogic when a communication is initiated;

[0029]FIG. 3b shows a flow chart of preferred steps taken by controllogic during a communication.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0030] Turning to FIG. 1, there is shown a graphical representation ofhow directional estimates for uplink and downlink paths vary, andultimately converge, with time. The x-axis (i.e. the abscissa)represents an averaging period and the y-axis (i.e. the ordinate)represents estimates of the uplink and downlink principal directionangle, φ. As can be seen, for very short averaging times (that is, thepoints towards the left hand side of the x-axis of the figure), theuplink and downlink directional estimates can be widely different. Thesedifferences arise from the different physical (and essentiallyinstantaneous) propagation paths from the base station (i.e. the antennaarray) to a subscriber unit and vice versa, with these differingpropagation paths partially attributable to any difference in carrierfrequency used to support the uplink and downlink channels. As eitherthe averaging period or the time is increased (illustrated by movementtowards the right-hand side of the x-axis of FIG. 1), the averagedirectional estimates for the uplink and downlink start convergingtoward a stable direction. That is to say, the uplink and downlinkdirections are the same if averaged over sufficient time, and thereforeaddress (and hence to smooth out) variations in the principal directionangle caused by, for example, any duplex frequency difference in afrequency division multiplexed (FDM) system or the like.

[0031]FIG. 2 is a block diagram of an adaptive antenna network 10according to a preferred embodiment of the invention. A plurality ofantenna elements 12 a-12 k, preferably physically separated byhalf-wavelengths for maximum aperture gain, make up a portion of theadaptive antenna array 14 responsive to uplink transmissions 16 a-16 kemanating from a subscriber unit 18, such as a mobile station or aterminal. Of course, the antenna elements 12 a-12 k maycontemporaneously service multiple subscriber units in a time divisionor code division basis, with a single subscriber 18 unit shown forexemplary purposes and clarity of the figure. The number of antennaelements with the adaptive antenna array 14 is arbitrary. The pluralityof antenna elements 12 a-12 k are generally associated or collocatedwith a base station 19.

[0032] Uplink signals 16 a-16 k received at the plurality of antennaelements 12 a-12 k are passed through low noise amplifiers (LNA) 20 a-20k, with individual LNAs generally associated with specific antennaelements. An automatic gain control (AGC) feedback loop, responsive torecovered uplink signals from the antenna elements 12 a-12 k and coupledto the LNAs 20 a-20 k for operational control thereof, is arranged toadjust gain within each LNA, thereby ensuring that a maximum dynamicrange of the antenna elements 12 a-12 k is utilised. Following the LNAs20 a-20 k, complex-weighting elements 24 a-24 k are arranged to applycomplex weights to each uplink signal from each antenna element 12 a-12k. The weights are derived from a control algorithm 26 operationallyresponsive to a signal processor 28 that itself receives gain adjustedversions 30 a-30 k of the uplink transmissions 16 a-16k.Weight-corrected signals from each of the complex weighting elements 24a-24 k are then linearly summed together in summing unit 32. As will beunderstood, the weights have a phase and angle such that a cleardirection θ_(u) can be established for the uplink direction by the basestation 19.

[0033] The signal processor 28 is also coupled to receive a resultantsignal 34 that is output from the summing unit 32. The signal processor28 and control algorithm 30 co-operate to estimate, using knownmethodologies, the uplink direction (θ_(u)) for the subscriber unit 18within a cell served by the base station 19 at which the adaptiveantenna network 10 is located. In particular, the signal processor 26and control algorithm may look to a feedback mechanism and adetermination of signal-to-noise levels for the various incident uplinksignals 16 a-16 k in order to calculate new weights for the complexweighting elements 24 a-24 k. Furthermore, the control algorithm 26 mayutilise a raw measure of the signal to noise ratio of each of the inputantenna elements 12 a-12 k (i.e. before application of complexweighting), thereby yielding an internal measure of performance for theapplied complex weights.

[0034] A direction of arrival (DOA) estimation unit 36 uses aconventional output metric 38 (readily appreciated by the skilledaddressee) from the signal processor 28 to determine/estimate adirection of arrival angle φ of significant energy in the uplink signals16 a-16 k. The directional of arrival angle φ is used to alter (complexphase and angle information of) downlink weighting elements 40 a-40 k,and thereby to steer transmitted signal energy (i.e. a baseband transmitsignal 42) in a predetermined direction in the downlink. The basebandtransmit signal 42, such as voice and/or data, passes through thesedownlink weighting elements 40 a-40 k before being amplified in poweramplifiers 46 a-46 k that are generally individually associated withspecific downlink antenna elements 48 a-48 k in a transmit portion ofthe adaptive antenna array 14.

[0035] Antenna elements (12 a-12 k and 48 a-48 k) associated withreceive and transmit paths can be either separate, dedicated elements(as illustrated in FIG. 2) or shared (common) antenna elements coupledto respective transmit and receive chains through a duplex filter (notshown).

[0036] When a call to or from the mobile is initiated, or when anothertype of communication between the base station and the mobile station isrequired, an equivalent downlink direction (θ_(d)) is assumed to be thesame as (i.e. complementary to) the uplink angle of arrival φ. Now,according to a preferred embodiment of the present invention, whenever adownlink communication is initiated, the number of antenna elementsincluded (from the array 14 to support the downlink channel 50) is small(for example one or two) giving a wide beam aperture. The use of a widebeam (and preferably also a predetermined power setting thatsignificantly curtails signal propagation beyond a serving cellboundary) therefore initially provides a system minimised interferenceenvironment whilst generally ensuring a minimum QoS to an addressedsubscriber unit. The wide beam may be omni-directional or sectorized.With the passage of time and preferably subject to an assessment of QoSto the subscriber unit (reported directly from downlink measurementstaken by the addressed subscriber unit), the width of the beam isnarrowed to focus the downlink transmission in the direction of thesubscriber unit. Furthermore, it will be recalled that, with the passageof time, convergence between directional estimates derived from theuplink and downlink occurs, and so beam width narrowing/alteration canoccur on the basis of both convergence and QoS indications, if desired.

[0037] A metric used to measure the Quality of Service provided by thedownlink is preferably C/(I+N), but a number of other QoS metrics, suchas the Frame Erasure Rate (FER) and bit error rate (BER), may be used(either individually or in combination).

[0038] According to a preferred embodiment of the present invention, ifthe QoS metric (such as C/(I+N) in the measured downlink) is determinedto be within a threshold of a previously set budget, the number ofantenna elements used in the adaptive array 14 can be increased by oneor more (subject, perhaps, to a level of confidence associated with thedirection), thereby narrowing the beam width. Since narrowing of thebeam knowingly occurs based on confidence in the direction of arrival ofuplink signals and/or QoS at the subscriber unit, the subscriber unit islikely to be serviceable within the narrowed beam and is unlikely todemand an increased power budget for downlink transmissions.Consequently, the system of the preferred embodiment will not be taskedto provide excessive (or increasing) power within a narrow beam width,and so the possibility of inter-cell interference is generally avoided.

[0039] The budget by which decisions are made may be set by the systemoperator or be specified in a technical standard used to define anoperating protocol for the system.

[0040] Clearly, the process of adding at least one antenna elementassumes that, at initiation (i.e. call set-up), the addressed subscriberunit is ostensibly within the beam aperture; this would also be the casewith an initial omni-directional transmission.

[0041] Conversely, should a sectorised approach to beam width beinitially adopted, then it is possible that an addressed subscriberunit, although contactable, is actually outside of the sectorised beam.In this instance, rather than increase power into the narrow beam, thepreferred embodiment increases beam width by decreasing the number ofantenna elements 12 a-12 k used for the downlink channel. With repeatedtaking of QoS measurements, the process of adding an antenna element isrepeated until such time as the C/(I+N), or other metric, improves to anacceptable level. The beam width is then preferably narrowed with timein view of convergence affects between uplink and downlink directionalestimates.

[0042] Alternatively or additionally, in the event of initial use of avariable beam-width, one could use a more critical approach to uplink todownlink angle of arrival (AOA) translation. If large AOA estimationerrors occur then, in one embodiment of the present invention, the useof the variable beam width can, in fact, compensate for the AOA error toavoid having to support an increase in downlink power for an acceptableQoS.

[0043] The C/(I+N) value may be measured by the mobile station atpredetermined intervals during the communication. If the downlinkC/(I+N) value moves below a predetermined threshold, the number ofantenna elements in the array may be reduced by one (or more), therebyincreasing the beam width. Likewise, if the C/(I+N) value (or othermetric) improves, the number of antenna elements may be increased byone. In this manner, the aperture of the beam is dynamically maintainedin an in-call scenario and such that the beam width is as narrow as thepredetermined QoS parameters of the system allows.

[0044] Selective active engagement/disengagement of the antenna elements48 a-48 k in the formation of the downlink beam can be controlled by theuse of processor-controlled switches within each path to the antennaelement, thereby providing absolute isolation. Preferably, switching ofthe antenna elements 48 a-48 k into and out of the array 14 is achievedby actively managing the downlink weighting elements such as to preventthe baseband transmit signal from being radiated from particularselected ones of the antenna elements 48 a-48 k.

[0045] In generality, the signal process 28 and the various control andestimation algorithms (26, 36) provide the necessary functionality toresolve management of the antenna array, as will be understood.

[0046]FIGS. 3a and 3 b in combination describe a preferred operatingmethodology in which antenna elements are added and subtracted from theantenna array 14 based, principally, on QoS metric measurements. Themethodology is generally applicable to both an in-call scenario and callestablishment according to the preferred embodiments of the presentinvention, and in this respect some of the process steps will beunnecessary dependent upon the initial premise on which the system isset-up.

[0047]FIG. 3a is a flow chart illustrating the steps taken by controllogic (of either a base station transceiver or a base stationsub-system) to manage an adaptive antenna array. The call is initiated60 with the adaptive array utilising 62 “x” antenna elements (where x isa positive integer). A downlink 64 is therefore established. The mobilestation performs some form a metric analysis 66 on the downlink, e.g.C/(I+N), and returns 68 the metric analysis to the base station for usethereby. Following return of the metric analysis, the base stationdetermines 68 whether the metric analysis is better or worse than alower operating limit of a QoS budget. In the negative 70 (i.e. the QoSis below a predetermined level), the number of antenna elements isdecreased 74 (by at least one), thereby widening the beam and flowproceeds to a decision block that determines whether the call (or thecommunication) is on-going. Clearly, if it is established that the callor connection has terminated, then the process ends 80. Steps 72 and 74may be omitted in a system initially using a suitably wide-area(sectorised or omni-directional) downlink transmission. An affirmativepath 78 from decision block 70 results in a consolidation of processflows at block 76.

[0048] In an on-going call/communication situation, further metricanalysis 82 is (preferably) undertaken by the subscriber unit andreported 84 to the base station, although it is contemplated thatchannel performance could be inferred from operational parameters at thebase station. A comparison between a previous metric and a subsequentmetric is undertaken to assess whether there has been any significantchange. If the metrics are relatively constant/approximate 88, then flowreturns to decision block 76, else an assessment 90 is made as towhether the most recent metric is better than the previous metric. Ifthere is an effective improvement in the metric (whereby the subscribermay be experiencing an improved QoS), then the system may operate toincrease 92 the number of antenna elements and hence to focus/narrow thedownlink beam. Of course, the improvement in the metric could also beattributable to convergence of directional estimates, although theeffect of narrowing the beam is the same regardless. Should the metricbe assessed to be worse 94, then the system preferably operates todecrease 96 the number of antenna elements and hence to widen thedownlink beam (rather than to increase down-link power, although this isclearly an option). Flow subsequent to either of process steps 92 and 96then returns to block 76 for determination of whether the call (or thecommunication, e.g. a control channel transmission) is on going.

[0049] In way of brief summary, a searching algorithm may be employedwithin the present invention (preferably in-call, although equallyapplicable to call establishment procedures) to direct an increasinglynarrow aperture downlink beam to be moved through progressively varyingangles and beam width, from an uplink directional estimate, by addingand subtracting certain antenna elements within an adaptive array.Alternatively, a wide beam may be narrowed, with the passage of time, tothe uplink angle of arrival estimate in view of convergence between theuplink and downlink directional estimates.

[0050] Beam oscillation is diagrammatically shown in FIG. 4 in which acellular system 100 is shown to include an adaptive antenna array 14(and associated base site control equipment 102) servicing a subscriberunit 18. Three downlink transmit lobes 102-106 are shown, withdirectional arrows on the narrowest lobe 104 and the widest lobe 108indicating that there needs to be an variation in the number of antennaelements used in the antenna array 14 to service the subscriber unit 18(at least initially during call set-up). In all likelihood, with timeand hence directional estimation convergence between the uplink, thenarrowest beam will ultimately be correctly aligned on the subscriberunit to minimise system interference.

[0051] It will, of course, be appreciated that the above description hasbeen given by way of example only and that modifications may be madewithin the scope of the present invention. Whilst the preferredembodiment has been described in relation to an adaptive antennanetwork, the underlying control logic could be provided in the form of acomputer program product, such as in the form of a CD-ROM or othersoftware agent that can upgrade existing antenna sites.

[0052] The present invention can be applied to both traffic and controlchannels, with the traffic being voice, data or a combination thereof,and is not limited to any particular form of communication protocol orair-interface.

1. An adaptive antenna arrangement for generating a downlink beam, theadaptive antenna arrangement comprising: a plurality of antennaelements; and a controller for controlling formation of the downlinkbeam, the controller arranged to adjust, with time, a number of antennaelements active in the formation of the downlink beam thereby to vary,in use, a beam width of the downlink beam.
 2. The adaptive antennaarrangement of claim 1, wherein the controller is operationallyresponsive to quality of service metrics of the downlink beam, andwherein the controller is arranged to vary the beam width depending uponthe quality of service metrics.
 3. The adaptive antenna arrangement ofclaim 2, wherein the controller is arranged to vary the beam widthdepending upon relative variations in the quality of service metrics. 4.The adaptive antenna arrangement of claim 1, 2 or 3, wherein thecontroller is arranged to vary the beam width and direction thereof inresponse to convergence between angle of arrival estimates for downlinkand uplink paths.
 5. The adaptive antenna arrangement of any precedingclaim, wherein the adaptive antenna arrangement, in use, initially formsan omni-direction beam.
 6. The adaptive antenna arrangement of anypreceding claim, further comprising a direction of arrival estimator andwherein the adaptive antenna arrangement, in use, initially forms asectorised beam based on an uplink angle of arrival estimate.
 7. Theadaptive antenna arrangement of any preceding claim, wherein thesectorised beam compensates for errors in directional estimation.
 8. Anadaptive antenna network providing downlink communication to a mobilestation, the adaptive antenna network comprising: two or more antennaelement adapted to be switched in and out of the adaptive antennanetwork as required; control logic for switching antenna elements in andout of the adaptive antenna network; a downlink communications channelfor downlink communication from the antenna network to the mobilestation, which channel can be measured by one or more Quality of Service(QoS) metrics and which channel is constrained to operate withinpredetermined QoS parameters; wherein the mobile station measures apredetermined QoS metric of the downlink communication and returns a QoSmeasure to the control logic; and wherein the control logic switches atleast one antenna element, if available, into the adaptive antennanetwork if the QoS measure is within the predetermined QoS parameters orswitches at least one antenna element, if available, out of the adaptiveantenna network if the QoS measure is outside the predetermined QoSparameters;
 9. The adaptive antenna network as claimed in claim 8,wherein one Quality of Service (QoS) metric measured is the channel tointerference ratio C/(I+N).
 10. A cellular communication systemcomprising: a base station having control logic responsible forestablishing and maintaining a downlink channel resource; an antennaarray comprising a plurality of antenna elements, the antenna array andthe plurality of antenna elements operationally responsive to thecontrol logic, the plurality of antenna elements, in use, radiating atleast one directional-orientated downlink channel resource therefrom andwherein formation of the at least one directional-orientated downlinkchannel resource is controlled by the control logic; and wherein thecontrol logic includes means for adjusting, with time, a number ofantenna elements active in the formation of the at least onedirectional-orientated downlink channel resource, thereby to vary, inuse, a beam width of the at least one directional-orientated downlinkchannel resource.
 11. The cellular communication system of claim 10,wherein the control logic includes means for contrasting quality ofservice metrics, and wherein the control logic is arranged to vary thebeam width depending upon the quality of service metrics.
 12. Thecellular communication system of claim 11, wherein the control logic isarranged to vary the beam width depending upon relative variations inthe quality of service metrics.
 13. The cellular communication system ofclaim 10, 11 or 12, wherein the control logic is arranged to vary thebeam width and direction thereof in response to convergence betweenangle of arrival estimates for downlink and uplink paths.
 14. Thecellular communication system of any of claims 10 to 13, wherein theantenna array, in use, initially forms an omni-direction beam.
 15. Thecellular communication system of any of claims 10 to 14, wherein thebase station includes an uplink angle of arrival estimator and whereinthe adaptive antenna arrangement, in use, initially forms a sectorisedbeam based on an uplink angle of arrival estimate.
 16. A controller foran adaptive antenna having a plurality of antenna elements configurable,in use, to form a directional downlink beam in response to thecontroller, the controller comprising: means for controlling formationof the downlink beam; and means for adjusting, with time, a number ofantenna elements active in the formation of the downlink beam thereby tovary, in use, a beam width of the downlink beam.
 17. The controller ofclaim 16, further comprising: means for contrasting quality of servicemetric measurements; and wherein the means for adjusting is arranged tovary the beam width depending upon the quality of service metrics. 18.The controller of claim 17, wherein the means for adjusting varies thebeam width depending upon relative variations in the quality of servicemetrics.
 19. The controller of claim 16, 17 or 18, further comprising:an uplink angle of arrival estimator; and wherein the means foradjusting varies the beam width and direction of the downlink beam inresponse to convergence between angle of arrival estimates for downlinkand uplink paths respectively derived and determined from the uplinkangle of arrival estimator.
 20. The controller of claim any of claims 16to 19, wherein the means for adjusting, in use, initially causesformation of an omni-direction beam.
 21. The controller of claim any ofclaims 16 to 19, wherein the means for adjusting, in use, initiallycauses formation of a sectorised beam based on an uplink angle ofarrival estimate.
 22. The controller of claim 21, wherein the sectorisedbeam compensates for errors in directional estimation.
 23. A method ofcontrolling downlink communication from an adaptive antenna to asubscriber unit, the adaptive antenna having a plurality of antennaelements the method comprising: controlling dispersion of a downlinkbeam by adjusting, with time, a number of antenna elements active in theformation of the downlink beam to vary, in use, a beam width of thedownlink beam.
 24. The method of claim 23, further comprising varyingthe beam width depending upon quality of service metrics measured by thesubscriber unit.
 25. The method of claim 24, further comprising varyingthe beam width depending upon relative variations in the quality ofservice metrics.
 26. The method of claim 23, 24 or 25, furthercomprising varying the beam width and direction thereof in response toconvergence between angle of arrival estimates associated with downlinkand uplink paths.
 27. The method of claim any of claims 23 to 26,further comprising: initially generating an omni-direction downlink beamat call establishment; and subsequently narrowing the downlink beam. 28.The method of claim any of claims 23 to 27, further comprising:estimating an angle of arrival; initially forming a sectorised beambased on an uplink angle of arrival estimate.
 29. The method of claim28, wherein the sectorised beam compensates for errors in directionalestimation.
 30. A method of providing downlink communication between anadaptive antenna and a mobile unit of a cellular communication system,the adaptive antenna having two or more switchable antenna elements andcontrol logic for actuating switching of said antenna elements in andout of the adaptive antenna network, the method comprising: establishinga downlink communications channel for downlink communication from theantenna network to the mobile unit and constraining the downlinkcommunication to operate within predetermined Quality of Service (QoS)parameters; measuring at the mobile station a predetermined QoS metricof the downlink communication and returning a QoS measure to the controllogic; and switching at least one antenna element, if available, intothe adaptive antenna network if the QoS measure is within thepredetermined QoS parameters or switching at least one antenna element,if available, out of the adaptive antenna network if the QoS measure isoutside the predetermined QoS parameters.
 31. The method as claimed inclaim 30, wherein one Quality of Service (QoS) metric measured is thechannel to interference ratio C/(I+N).
 32. A computer program elementcomprising computer program code means to make a control logic of amulti-element adaptive antenna array execute procedure to perform thesteps of any of claims 23 to
 31. 33. The computer program element ofclaim 32, embodied on a computer readable medium.